1. Field of the Invention
The present invention relates to a driving circuit for a gyroscope, and particularly to a driving circuit for a gyroscope which generates a driving signal of the gyroscope by a feedback signal of the gyroscope such as a vibratory gyroscope capable of detecting a rotational angular velocity.
2. Description of the Prior Art
FIG. 7 is a block diagram showing an example of a conventional vibratory gyroscope which is a background of the present invention. The vibratory gyroscope 1 comprises a vibrator 2 which includes, for example, a triangular prism-shaped vibrating body 3. On three side faces of the vibrating body 3, piezoelectric elements 4a, 4b and 4c are formed respectively. One piezoelectric element 4a is used for feedback, and the other two piezoelectric elements 4b and 4c are used for driving and detecting.
Between the feedback piezoelectric element 4a and the two driving and detecting piezoelectric elements 4b and 4c, a driving circuit 7 consisting of an oscillation circuit 5 and a phase-shifting circuit 6 is connected.
Also, to the driving and detecting piezoelectric elements 4b and 4c, a detecting circuit 8 consisting of a differential amplifier and so on is connected.
In the vibratory gyroscope 1, the driving circuit 7 gives, by the feedback signal from one feedback piezoelectric element 4a of the vibrator 2, a constant voltage driving signal to the two driving and detecting piezoelectric elements 4b and 4c to vibrate the vibrating body 3.
When the vibrator 2 is rotated in such a state where the vibrating body 3 is vibrated, the output difference responsive to the rotational angular velocity is produced between the two driving and detecting piezoelectric elements 4b and 4c. A signal responsive to the output difference is output from the detecting circuit 8, and the rotational angular velocity is detected by the output signal.
However, in the vibratory gyroscope shown in FIG. 7, since the vibrator is driven by the driving signal which is constant voltage, when an output transformation efficiency of the vibrator (piezoelectric element), a capacity of the piezoelectric element, Q of the vibrator and so on change by the temperature change and changes with the lapse of time, sensitivity of the gyroscope (detecting circuit) fluctuates and the rotational angular velocity can not be detected accurately.